This invention relates to method and apparatus for determining melt index values for substances such as polymers, and in particular to a new method and apparatus for automatically determining such melt index values. In the present art, in order to conduct quality control on thermoplastics, the melt index value for the thermoplastic must be determined by a cumbersome and complicated manual process involving melting an amount of the substance, extruding it through an orifice, and determining the melt index for the extrudate. Such a manual process is set forth, for instance, in the American Society for Testing and Materials (ASTM) Designation D1238-85 entitled "Standard Test Method for Flow Rates of Thermoplastics by Extrusion Plastometer," which is incorporated herein by reference.
Where many thermoplastics must be tested, the present method and apparatus are inadequate, because they are slow, expensive and labor-intensive. Accordingly, a need has arisen for a fast, reliable automatic melt indexing method and apparatus.
Another disadvantage of the method and apparatus presently in use is that there is danger to the operator of coming into contact with heating units and molten thermoplastics. It is therefore an object of this invention to provide a melt index testing method and apparatus which minimize the risk of injury to workers.
When an operator of manual melt indexing apparatus conducts a test, several operations must be performed, including setting up a cylindrical cartridge with the test substance, melting the substance to form a molten resin, beginning the extrusion process by placing a weight so that it bears down on the resin, timing the extrusion rate through a given distance by using a stop watch or other timer, cutting off the extrudate with a screwdriver or blade, removing the used extrudate, etc. Another form of the test involves extruding the resin for a predetermined amount of time, and then weighing the extrudate to determine the melt index. Either of these involves many actions and chances for error on the part of the operator, and thus imprecision is a common problem in the field.
Accordingly, it is an object of this invention to provide a method and apparatus for automatic melt index testing, requiring little labor and providing high reliability, and in particular to provide such a method and apparatus which yield precise and highly repeatable results.
It is another object of the invention to provide such a method and apparatus which can be used for automatically testing a large number of thermoplastics without intervention by the operator.